Growing III-V Compound Semiconductors from Trenches Filled with Intermediate Layers

ABSTRACT

A method of forming an integrated circuit structure includes forming an insulation layer over at least a portion of a substrate; forming a plurality of semiconductor pillars over a top surface of the insulation layer. The plurality of semiconductor pillars is horizontally spaced apart by portions of the insulation layer. The plurality of semiconductor pillars is allocated in a periodic pattern. The method further includes epitaxially growing a III-V compound semiconductor film from top surfaces and sidewalls of the semiconductor pillars.

This application is a divisional of U.S. patent application Ser. No.12/842,221, entitled “Growing III-V Compound Semiconductors fromTrenches Filled with Intermediate Layers,” filed on Jul. 23, 2010, whichapplication claims the benefit of U.S. Provisional Application No.61/262,042 filed on Nov. 17, 2009, entitled “Growing III-V CompoundSemiconductors from Trenches Filled with Intermediate Layers,” whichapplication is hereby incorporated herein by reference.

TECHNICAL FIELD

This disclosure relates generally to integrated circuit manufacturingprocesses, and more particularly to forming group-III group-V (III-V)compound semiconductor films.

BACKGROUND

Group-III group-V compound semiconductors (often referred to as III-Vcompound semiconductors) such as gallium nitride (GaN) and their relatedalloys have been under intense research in recent years due to theirpromising applications in electronic and optoelectronic devices.Particular examples of potential optoelectronic devices employing III-Vcompound semiconductors include blue light emitting diodes and laserdiodes, and ultra-violet (UV) photo-detectors. The large bandgap andhigh electron saturation velocity of many III-V compound semiconductorsalso make them excellent candidates for applications in high temperatureand high-speed power electronics.

Epitaxially grown GaN films are widely used for in the fabrication oflight-emitting diodes. Unfortunately, epitaxial GaN films must be grownon substrates other than GaN because it is extremely difficult to obtainGaN bulk crystals due to the high equilibrium pressure of nitrogen atthe temperatures typically used to grow bulk crystals. Owing to the lackof feasible bulk growth methods for GaN substrates, GaN is commonlydeposited epitaxially on dissimilar substrates such as silicon, SiC andsapphire (Al₂O₃). However, the growth of GaN films on dissimilarsubstrates is difficult because these substrates have lattice constantsand thermal expansion coefficients different than that of GaN. If thedifficulties in the growth of GaN films on silicon substrates could beovercome, silicon substrates would be attractive for GaN growth giventheir low cost, large diameter, high crystal and surface quality,controllable electrical conductivity, and high thermal conductivity. Theuse of silicon substrates would also provide easy integration of GaNbased optoelectronic devices with silicon-based electronic devices.

Additionally, due to the lacking of appropriate substrates for growingGaN films thereon, the sizes of the GaN films are limited. The highstresses created by growing a GaN film on a dissimilar substrate maycause the substrate to bow. This may cause several adverse effects.Firstly, a great number of defects (dislocations) will be generated inthe supposedly crystalline GaN films. Secondly, the thicknesses of theresulting GaN film will be less uniform, causing wavelength shifts ofthe light emitted by the optical devices formed on the GaN films.Thirdly, cracks may be generated in large stressed GaN films.

SUMMARY

In accordance with one aspect of the embodiment, a method of forming anintegrated circuit structure includes forming an insulation layer overat least a portion of a substrate; forming a plurality of semiconductorpillars over a top surface of the insulation layer. The plurality ofsemiconductor pillars is horizontally spaced apart by portions of theinsulation layer. The plurality of semiconductor pillars is allocated ina periodic pattern. The method further includes epitaxially growing aIII-V compound semiconductor film from top surfaces and sidewalls of thesemiconductor pillars.

Other embodiments are also disclosed.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the embodiments, and the advantagesthereof, reference is now made to the following descriptions taken inconjunction with the accompanying drawings, in which:

FIGS. 1A through 8 illustrate cross-sectional views, a perspective view,and a top view of intermediate stages in the manufacturing of a III-Vsemiconductor film in accordance with an embodiment; and

FIG. 9 through 18 are cross-sectional views and a perspective view ofintermediate stages in the manufacturing of III-V semiconductor films inaccordance with alternative embodiments.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of the embodiments of the disclosure are discussedin detail below. It should be appreciated, however, that the embodimentsprovide many applicable inventive concepts that can be embodied in awide variety of specific contexts. The specific embodiments discussedare merely illustrative of specific ways to make and use theembodiments, and do not limit the scope of the disclosure.

A novel method for forming group-III group-V (referred to as III-Vhereinafter) compound semiconductor films is provided. Throughout thedescription, the term “III-V compound semiconductor” refers to compoundsemiconductor materials comprising at least one group-III element andone group-V element. The term “III-N compound semiconductor” refers to aIII-V compound semiconductor comprising nitrogen. The required stages ofmanufacturing an illustrative embodiment are illustrated. Those skilledin the art will recognize that other manufacturing steps may need totake place before or after the described stages in order to produce acomplete device. Throughout the various views and illustrativeembodiments of the disclosure, like reference numbers are used todesignate like elements.

Referring to FIG. 1A, substrate 20 is provided. In an embodiment,substrate 20 is a bulk substrate comprising, for example, semiconductormaterial(s) such as silicon. Substrate 20 may be formed of othercommonly used materials such as sapphire, SiGe, SiC, Ge, or the like.Insulation regions 22 (which may be considered as portions of aninsulation layer) are formed in substrate 20. In an embodiment, theinsulation regions may include shallow trench isolation (STI) region(s)22, and hence are referred to as STI regions 22 throughout thedescription. The formation process of STI regions 22 may includerecessing portions of substrate 20, and filling the resulting recesseswith a dielectric material, followed by a chemical mechanical polish(CMP) to remove excess dielectric material. The remaining portions ofthe dielectric material form STI regions 22. In the resulting structure,substrate 20 may include portion 20_1 that is below the bottom surfacesof STI regions 22, and portions 20_2 that are between, and separatedfrom each other by, STI regions 22. It is noted that although STIregions 22 were originally formed in substrate 20, substrate portion20_1 may also be treated as a substrate, while STI regions 22 may betreated as being over substrate 20_1.

FIG. 1B illustrates a top view of the structure shown in FIG. 1A,wherein the cross-sectional view in FIG. 1A is obtained from the planecrossing line 1A-1A in FIG. 1B. From the top view, it is observed thatsubstrate portions 20_2 are arranged in a periodic pattern. In anexemplary embodiment as shown in FIG. 1B, substrate portions 20_2 arearranged as an array, in other embodiments, substrate portions 20_2 maybe arranged in other patterns such as a hexagon pattern. Distance Dbetween neighboring substrate portions 20_2 may be less than about 5 μm,and may also be between about 20 nm and about 5 μm. The length and/orwidth L of substrate portions 20_2 (which will also be the length and/orwidth of the resulting semiconductor re-growth regions 28 and(semiconductor) pillars 30, as shown in FIG. 5A) may be smaller thanabout 5 μm. One skilled in the art will realize, however, that thedimensions recited throughout the description are merely examples, andwill change if different formation technologies are used. From the topview, substrate portions 20_2 may have the shape of square, rectangle,circle, hexagon, octagon, or the like.

Referring to FIG. 2, substrate portions 20_2 are removed partially orfully, forming recesses 26. In an embodiment as shown in FIG. 2,V-grooves may be formed at the bottom of recesses 26, so that theexposed surface of silicon substrate 20 in recesses 26 have (111)surface orientations. In alternative embodiments, as shown with dottedlines, the bottom surfaces of recesses 26 may be substantially flat.

Next, as shown in FIG. 3, semiconductor re-growth regions 28 areepitaxially grown in recesses 26. Semiconductor re-growth regions 28 maybe formed of a material having a lattice constant between the latticeconstant of substrate 20 and the lattice constant of the overlying III-Vsemiconductor film 32 (not shown in FIG. 3, please refer to FIG. 6). Inan embodiment, semiconductor re-growth regions 28 comprise bufferregions 28_1 and top regions 28_2. Buffer regions 28_1 may be formed ofAlN, low temperature GaAs, or a low temperature GaAs and a hightemperature GaAs on the low temperature GaAs. The low temperature GaAsmay be epitaxially grown at a temperature lower than about 400° C.,while the high temperature GaAs may be epitaxially grown at atemperature higher than about 600° C. Alternatively, buffer regions 28_1may be formed of a low temperature GaN or AN, which may be epitaxiallygrown at a temperature lower than about 850° C. Top regions 28_2 may beformed of GaN, which may be epitaxially grown at a temperature higherthan about 1100° C. By growing semiconductor re-growth regions 28 inrecesses 26, the threading dislocations may be blocked by the sidewallsof STI regions 22, so that fewer defects will occur in subsequentlyformed III-V semiconductor film 32 (FIG. 6). Next, a CMP is performed toremove excess semiconductor re-growth regions 28. The resultingstructure is shown in FIG. 4.

FIG. 5A illustrates the recessing of STI regions 22. As a result, theportions of re-growth regions 28 over the top surfaces of remainingportions of STI regions 22 form pillars 30. The height H of pillars 30may be greater than about 50 nm, or even greater than about 100 nm. FIG.5B illustrates a perspective view of the structure shown in FIG. 5A.

Referring to FIG. 6, III-V compound semiconductor film 32 is epitaxiallygrown. In an embodiment, III-V compound semiconductor film 32 comprisesGaAs, although it may also be formed of other III-V compoundsemiconductor materials such as GaN, InN, AlN, InP, or the like. WithIII-V compound semiconductor film 32 grown from the top surface andsidewalls of pillars 30, the defect density in III-V compoundsemiconductor film 32 may be reduced. A planarization (for example, aCMP) may then be performed to flatten the top surface of III-V compoundsemiconductor film 32.

Optionally, as shown in FIG. 7, mask layer 34 is formed on III-Vcompound semiconductor film 32. Mask layer 34 may include a materialselected from dielectric materials such as silicon nitride or siliconoxide. Mask layer 34 may also include multi-layers of theabove-discussed materials. The applicable deposition methods for formingmask layer 34 include physical vapor deposition (PVD) and chemical vapordeposition (CVD).

Mask layer 34 is patterned so that the top surface of III-V compoundsemiconductor film 32 is selectively exposed through the gaps betweenremaining portions of mask layer 34. The patterning may be performedusing a dry etch and/or a wet etch. The remaining portions of mask layer34 may have any pattern with controlled width and spacing, and may formparallel strips. In other embodiments, the remaining portions of masklayer 34 may be arranged as an array or other periodic patterns, witheach remaining portion having a square, a strip, or a polygon shape (ina top view). In yet other embodiments, the remaining portions of masklayer 34 may form an interconnected grid structure, with windows thereinfor exposing the underlying III-V compound semiconductor film 32. Thethickness T of mask layer 34 may be about 2 nm to about 6 μm.

Next, as shown in FIG. 8, an additional III-V semiconductor film 36 isgrown on the exposed surface of III-V compound semiconductor film 32,for example, using epitaxial layer overgrowth (ELOG). With the formationof mask layer 34 and the ELOG step, the defect density in III-Vsemiconductor film 36 is lower than in III-V compound semiconductor film32. In an embodiment, III-V semiconductor film 36 may be formed of asame material as that of III-V compound semiconductor film 32, forexample, GaN. Alternatively, III-V semiconductor films 32 and 36 may beformed of different materials, for example, III-V compound semiconductorfilm 32 may be formed of GaAs, while III-V semiconductor films 36 may beformed of GaN. In subsequent process steps, III-V semiconductor film 36may be planarized. Further, the underlying substrate 20 and STI regions22 may be removed, for example, using CMP. The resulting structure isthus a bulk III-V substrate (for example, a GaN substrate) with a lowdefect density.

FIGS. 9 through 11 illustrate an alternative embodiment. Unlessspecified otherwise, like reference numerals in this embodiment (andsubsequently discussed embodiments) represent like components in theembodiment shown in FIGS. 1A through 8. Accordingly, the process stepsand applicable materials may not be repeated herein. The initial stepsof this embodiment are essentially the same as shown in FIGS. 1A through2. Next, as shown in FIG. 9, semiconductor re-growth regions 28 areformed in the form of a single layer, with the top portions and thebottom portions formed of a same semiconductor material. In anembodiment, semiconductor re-growth regions 28 are formed of epitaxialGaAs.

Referring to FIG. 10, STI regions 22 are recessed, so that pillars 30,which extend above the top surfaces of STI regions 22, are formed. Insubsequent steps, III-V compound semiconductor film 32 is formed, asshown in FIG. 11. Optionally, III-V semiconductor film 36 is formed. Theprocess steps and the materials of III-V semiconductor films 32 and 36may be essentially the same as shown in FIGS. 7 and 8 and the respectivediscussion, and hence are not repeated herein.

FIGS. 12 through 14 illustrate yet another embodiment. The initial stepsof this embodiment are essentially the same as shown in FIGS. 1A through2. Next, as shown in FIG. 12, semiconductor re-growth regions 28 areformed. Semiconductor re-growth regions 28 may be composite regionscomprising buffer regions 28_1 and top regions 28_2, as shown in FIG. 3,or regions formed of a single material, as shown in FIG. 9. In anembodiment, semiconductor re-growth regions 28 are formed of epitaxialGaAs, although other semiconductor materials such as GaN may be used.Next, as shown in FIG. 13, an isotropic etch is performed tosemiconductor re-growth regions 28, for example, using KOH, so thatV-grooves 40 are formed. The exposed surfaces of semiconductor re-growthregions 28 may have (111) surface planes. In the embodiments in whichre-growth regions 28 are formed of GaAs, the (111) surface planes mayhave a smaller lattice mismatch with the overlying III-V compoundsemiconductor film 32 (which may be formed of GaN, for example, see FIG.14) than the flat top surfaces of semiconductor re-growth regions 28 asshown in FIG. 12. As a result, fewer defects may be generated in thesubsequently formed III-V compound semiconductor film 32. Next, III-Vcompound semiconductor film 32 is formed, as shown in FIG. 14. Processsteps as shown in FIGS. 7 and 8 may then be performed to form III-Vsemiconductor film 36.

FIGS. 15A through 16 illustrate yet another embodiment. The initialsteps of this embodiment are essentially the same as shown in FIGS. 1Athrough 2. Next, as shown in FIG. 15A, semiconductor re-growth regions28 are formed. Semiconductor re-growth regions 28 may be compositeregions comprising buffer regions 28_1 and top regions 28_2, as shown inFIG. 3, or a formed of a single layer, as shown in FIG. 9. In anembodiment, top regions 28_2 are formed of epitaxial GaN, although othermaterials such as GaAs may be used. The partial pressures of processgases, temperature, and formation time may be adjusted, so that pyramids42 are formed, wherein pyramids 42 may have bases substantially levelwith the top surfaces of STI regions 22. The exposed surfaces (slopes)of semiconductor re-growth regions 28 may have the (111) surface-planes.FIG. 15B illustrates the perspective view of the structure shown in FIG.15A.

Next, as shown in FIG. 16, III-V compound semiconductor film 32 isepitaxially grown. III-V compound semiconductor film 32 and top regions28_2 may be formed of a same material or different materials. With III-Vcompound semiconductor film 32 grown starting from the slopes ofpyramids 42, the threading dislocations in III-V compound semiconductorfilm 32 may bend toward, and end at, the top surfaces of STI regions 22.As a result, fewer defects will be generated in III-V compoundsemiconductor film 32. In the embodiment III-V compound semiconductorfilm 32 and top regions 28_2 are formed of a same material such as GaN,III-V compound semiconductor film 32 may be formed at a temperaturehigher than the temperature for forming top regions 28_2.

FIGS. 17 and 18 illustrate yet another embodiment. The initial steps ofthis embodiment are essentially the same as shown in FIGS. 1A and 1B.Next, as shown in FIG. 17, STI regions 22 are recessed, so that the topportions 20_2 of substrate 20 form pillars 30. Next, III-V compoundsemiconductor film 32 is epitaxially grown, as shown in FIG. 18. Theprocess steps as shown in FIGS. 7 and 8 may then be optionallyperformed.

In the above-discussed embodiments, by starting the growth of III-Vcompound semiconductor film 32 from periodic patterned semiconductorre-growth regions 28, the defect numbers in the resulting III-V compoundsemiconductor film 32 may be reduced. Further, with the top surface ofre-growth regions 28 being V-grooves 40 or pyramids 42, the defectnumbers may be further reduced.

Although the embodiments and their advantages have been described indetail, it should be understood that various changes, substitutions andalterations can be made herein without departing from the spirit andscope of the embodiments as defined by the appended claims. Moreover,the scope of the present application is not intended to be limited tothe particular embodiments of the process, machine, manufacture, andcomposition of matter, means, methods and steps described in thespecification. As one of ordinary skill in the art will readilyappreciate from the disclosure, processes, machines, manufacture,compositions of matter, means, methods, or steps, presently existing orlater to be developed, that perform substantially the same function orachieve substantially the same result as the corresponding embodimentsdescribed herein may be utilized according to the disclosure.Accordingly, the appended claims are intended to include within theirscope such processes, machines, manufacture, compositions of matter,means, methods, or steps. In addition, each claim constitutes a separateembodiment, and the combination of various claims and embodiments arewithin the scope of the disclosure.

What is claimed is:
 1. A method comprising: forming an insulation layerextending into a substrate, with portions of the substrate in, andseparate from each other by, portions of the insulation layer; removingthe portions of the substrate to form recesses in the insulation layer;epitaxially growing a semiconductor material in the recesses; performinga planarization to remove excess portions of the semiconductor material,with remaining portions of the semiconductor material in the recesses;etching the remaining portions to form V-grooves; and epitaxiallygrowing a III-V compound semiconductor film starting from the V-grooves.2. The method of claim 1, wherein the remaining portions comprise GaAs,and wherein the III-V compound semiconductor film comprises GaN.
 3. Themethod of claim 1, wherein exposed top surfaces of the remainingportions in the V-grooves have (111) surface orientations.
 4. The methodof claim 1, wherein when the epitaxially growing the III-V compoundsemiconductor film is started, top ends of the V-grooves join topcorners of the insulation layer, with the top corners formed between atop surface of the insulation layer and sidewalls of the recesses. 5.The method of claim 1, wherein the epitaxially growing the semiconductormaterial comprises growing buffer regions, and growing top regions overthe buffer regions, and wherein the top regions are formed of differentmaterials than the buffer regions.
 6. The method of claim 1 furthercomprising: forming a patterned mask layer over the III-V compoundsemiconductor film, with portions of the III-V compound semiconductorfilm exposed through the patterned mask layer; and epitaxially growingan additional III-V compound semiconductor film from the exposedportions of the III-V compound semiconductor film.
 7. A methodcomprising: forming an insulation layer extending into a semiconductorsubstrate, with portions of the semiconductor substrate in, and separatefrom each other by, portions of the insulation layer, and wherein theportions of the substrate semiconductor form a repeated pattern;removing the portions of the substrate to form recesses in theinsulation layer; epitaxially growing a first III-V compoundsemiconductor in the recesses; performing a planarization to removeexcess portions of the first III-V compound semiconductor, withremaining portions of the first III-V compound semiconductor in therecesses and lower than a top surface of the insulation layer; etchingthe remaining portions to form V-grooves; and epitaxially growing asecond III-V compound semiconductor starting from the V-grooves.
 8. Themethod of claim 7, wherein the first III-V compound semiconductor andthe second III-V compound semiconductor are the same as each other. 9.The method of claim 7, wherein the first III-V compound semiconductorand the second III-V compound semiconductor are different from eachother.
 10. The method of claim 7, wherein exposed top surfaces of theremaining portions in the V-grooves have (111) surface orientations. 11.The method of claim 7, wherein when the epitaxially growing the secondIII-V compound semiconductor is started, top ends of the V-grooves jointop corners of the insulation layer, with the top corners formed betweena top surface of the insulation layer and sidewalls of the recesses. 12.The method of claim 7, wherein the remaining portions comprise bufferregions, and top regions over the buffer regions, and wherein the topregions are formed of different materials than the buffer regions. 13.The method of claim 7 further comprising: forming a patterned mask layerover the second III-V compound semiconductor, with portions of thesecond III-V compound semiconductor exposed through the patterned masklayer; and epitaxially growing an third III-V compound semiconductorfrom the exposed portions of the second III-V compound semiconductor.14. A method comprising: forming an insulation layer in a substrate,with portions of the substrate in, and separate from each other by, theinsulation layer; removing the portions of the substrate to formrecesses in the insulation layer; epitaxially growing a semiconductormaterial in the recesses to form semiconductor re-growth regions,wherein top ends of the semiconductor re-growth regions form pyramids;and epitaxially growing a III-V compound semiconductor film startingfrom the pyramids.
 15. The method of claim 14, wherein the semiconductorre-growth regions and the III-V compound semiconductor film compriseGaN.
 16. The method of claim 14, wherein surfaces of the pyramids have(111) surface orientations.
 17. The method of claim 14, wherein bases ofthe pyramids are substantially level with a top surface of theinsulation layer.
 18. The method of claim 14, wherein the semiconductorre-growth regions comprise buffer regions, and top regions over thebuffer regions, and wherein the top regions are formed of differentmaterials than the buffer regions.
 19. The method of claim 18, whereintop surfaces of the buffer regions are lower than a top surface of theinsulation layer.
 20. The method of claim 14 further comprising: forminga patterned mask layer over the III-V compound semiconductor film, withportions of the III-V compound semiconductor film exposed through thepatterned mask layer; and epitaxially growing an additional III-Vcompound semiconductor film from exposed portions of the III-V compoundsemiconductor film.